_Foot-prints of Lower Carboniferous reptiles in the United States._--I have stated, at p. 340., that in 1849, Mr. Isaac Lea observed the foot-marks of a large reptile in the lowest beds of the coal formation at Pottsville, about seventy miles N.E. of Philadelphia. These researches have since been carried farther by Professor H. D. Rogers, in the same region of anthracitic coal, lying on the eastern flank of the Alleghany Mountains. Beneath the productive coal-measures of that country occurs a dense mass of red shales and sandstones, which correspond nearly in position to the millstone grit and Mountain Limestone of the south-east of England. In these beds foot-prints, referred to three species of quadrupeds, have lately been detected, all of them five-toed and in double rows, with an opposite symmetry, as if made by right and left feet, while they likewise display the alternation of fore foot and hind foot. One species, the largest of the three, presents a diameter for each foot-print of about two inches, and shows the fore and hind feet to be nearly equal in dimensions. It exhibits a length of stride of about nine inches, and a breadth between the right and left treads of nearly four inches. The impressions of the hind feet are but little in the rear of the fore feet. The animal which made them is supposed to have been allied to a Saurian, rather than to a Batrachian or Chelonian; but more information is required before so difficult a point can be decided. With these foot-marks were seen shrinkage cracks, such as are caused by the sun's heat in mud, and rain-spots, with the signs of the trickling of water on a wet, sandy beach; all confirming the conclusion derived from the foot-prints, that the quadrupeds belonged to air-breathers, and not to aquatic races.[xii-A] The Cheirotherian foot-prints, figured by me at p. 338., in which the fore and hind feet are very unequal in size, betoken a distinct genus, and occur in the midst of the productive coal measures, being consequently less ancient.